The modern analog cellular system for mobile wireless duplex voice transmission called "Advanced Mobile Phone Service" (AMPS), uses the FCC assigned carrier frequency range of 800 to 900 MHz. Automobile-mounted cellular units transmit voice signals to a cellular base station within a given cell at up to one watt of power. Battery powered, hand-held cellular units transmit voice signals to a cellular base station within a given cell using up to one quarter watt of transmission power.
Despite the relatively low power output of the hand-held subscriber station, sustained power use and resulting decreased battery life is a major problem. Since a battery in a standard subscriber terminal is expected to last approximately one month, additional power drainage resulting in loss of battery life imposes substantial hardship on any subscriber using a portable handset. This problem is one of the major issues confronting designers of cellular handsets and systems today.
Conventional cellular subscriber stations are capable of communicating on at least one of two independent sets of frequencies. However, a conventional cellular base system normally communicates on only one of these two sets of frequencies. Thus, a cellular base system may be referred to as an "A" system if it uses one set of frequencies or a "B" system if it uses the other set of frequencies. This dual-system approach to radiotelephony results from regulations which are intended, at least in part, to promote competition in providing radiotelephone services.
When "A" and "B" cellular systems are both located in a single geographic area, radiotelephone service customers may choose to subscribe to either the "A" or "B" system in accordance with which system provides the best value to the customer. "B" systems are often referred to as "wireline" carriers because "B" systems are typically operated by 'the companies that provide wireline telecommunication services where the "B" systems are located. "A" systems are often referred to as non-wireline carriers because they are operated by companies other than the companies that operate the competing "B" systems. These frequency allocations are not necessarily permanent.
Each frequency set in a given cellular service area is assigned to one and only one carrier. However, in different service areas the same frequency set may be assigned to different carriers (much as a television channel may be assigned to an affiliate of one network in one city and to an affiliate of another network in another city).
The home frequency set of a given telephone unit is the set of frequencies which the unit will ordinarily attempt to use. This will depend in large part on which carrier is subscribed to by the telephone unit's user: if the user is a subscriber of a nonwireline carrier, the user's home frequency set will be the "A" frequencies, and vice versa.
As is well-known to those of ordinary skill in this field, a frequency set typically includes paging channels and associated signalling or control channels, as well as voice channels. The paging and control channels are used for preliminary coded communications between a cellular telephone and a cell site or base station in setting up a telephone call, after which a voice channel is assigned for the telephone's use on that call.
Each cellular carrier broadcasts a unique System Identification Number (SID) on all paging channels of the frequency sets on which it provides service in a given service area. A suitably equipped cellular subscriber station can thus determine which carrier is providing service on a given paging channel by identifying the SID. Usually the SID contains three digits.
Identification of a home SID is not necessarily required to be able to place a cellular call. Many carriers have reciprocal billing arrangements with one another, meaning that a call can be placed on a frequency associated with a non-home cellular system. However, use of a non-home carrier in this manner to place a call may result in the imposition of a surcharge (e.g., a fixed surcharge or a higher per-unit rate).
Furthermore, if the non-home carrier does not have a reciprocal billing arrangement with the user's home carrier, as a practical matter the user may not be able to place a call at all. Even though the telephone unit is capable of establishing a connection via the carrier signal, the non-home carrier's switching equipment typically will not allow the user to do anything with the connection without a way to bill the user for his or her usage. Some carriers automatically switch calls of this kind to an operator who can take down a credit card number. However, absent a billing arrangement of some kind, no call can be completed.
When a customer subscribes to a cellular system (either an "A" or "B" system), that system becomes the subscriber/customer's home system. The company that operates a customer's home system collects billing information and bills the customer for the customer's use of the home system's radiotelephone services. Whenever a customer is operating his or her cellular subscriber stations on a system other than the customer's home system, the customer is engaging in an activity known as roaming. The cellular system upon which a roaming cellular subscriber station is operating is viewed as a foreign system.
Subscribers may receive cellular telecommunication services while roaming. However, the home cellular carrier and the foreign cellular carrier must cooperate with one another before roaming services are permitted. For example, the foreign system must transfer call record information to the home system, and the home system must bill for, collect funds for, and distribute funds back to the foreign system for the roaming telecommunication services. Accordingly, the customer must typically pay additional charges when the customer uses roaming services.
When the customer operates his or her cellular subscriber station in the area covered by the cellular subscriber's home system, no serious cellular base system selection choice needs to be made. The customer will almost always want to use the home system because the charges for home-system telecommunication services will be less. On the other hand, when the customer is roaming away from the home system, a choice of whether to operate a cellular subscriber station on an "A" or "B" foreign system must be made.
Conventional cellular subscriber station handsets employ any one of several different programmable selection processes in choosing a cellular system upon which to operate. For example, a cellular subscriber station may prefer an "A" system but accept a "B" system if an "A" system is not available. This is called an "A/B" selection process. Conversely, a cellular subscriber station may prefer a "B" system but accept an "A" system if a "B" system is not available. This is called a "B/A" selection process. Alternatively, a cellular subscriber station may select only "A" systems ("A"-Only) or only "B" systems ("B"-Only) regardless of whether a competing system is available. Furthermore, a cellular subscriber station may select only the home system so that roaming is prohibited. Other selection processes may be implemented as well. A cellular subscriber station will typically utilize a default selection process which is consistent with its home system. For example, if a cellular subscriber station's home system is an "A" system, then the cellular subscriber station will typically utilize the "A"-Only or "A/B" selection processes as a default selection process.
Conventional cellular subscriber station handsets permit alteration of the default selection process. However, this feature is not often used by customers because it is difficult to accomplish through a cellular subscriber's station handset and because an intelligent nondefault selection process setting requires an understanding of cellular radiotelephony that many customers do not possess. Accordingly, providers of cellular services recognize that, for the most part, customers do not alter the default process selection setting.
The default selection process setting tends to limit any benefits that competition between "A" and "B" systems may provide while roaming. While the default setting favors the home system, at the same time it favors approximately one half of the numerous potential foreign systems over the other half of potential foreign systems. Assuming that this default setting does not change, in providing radiotelephone services to roaming customers one of each foreign area's two competing cellular systems benefits from an equipment-caused bias. As a result, the favored foreign systems need not aggressively price roaming services, and they need not be exceptionally cooperative with a roamer's home system, because it is highly probable that a roamer will use the favored foreign system regardless of cost. Consequently, roaming costs to a customer remain undesirably high.
While conventional cellular subscriber's station handsets can be configured so that the default system selection process setting is easily alterable, such configurations do not solve the problems faced by roaming customers. A typical customer is not prepared to make, or interested in making, a purchasing decision with respect to telecommunication services every time he or she is roaming. While roaming, a customer is unlikely to know the rates charged by the competing foreign cellular systems. Moreover, the rate structures may be complicated, and they may change from time to time. Thus, when a customer is roaming, he or she typically does not possess sufficient information upon which to base an intelligent foreign cellular system selection decision, even if the cellular subscriber station has the capacity for such a selection. Typically the subscriber does not desire to go to the time and trouble to obtain this information, and make the necessary alterations in the operation of the cellular subscriber station.
Further, the time required by the subscriber to make the aforementioned selections requires an expenditure in energy, and a resulting decrease in battery life. Consequently, a need exists for an efficient technique for channel selection that carries out the desires of the roaming subscriber. Even if the channel selection is limited between only the "A" and "B" bands, there are additional options that can be selected by the cellular subscriber. These further complicate the selection process which is carried out in the high-power AMPS mode of communication.
One such additional option for the aforementioned band selection is constituted by a personal communication system (PCS). When this type of system is used, predetermined frequencies (in addition to the "A" and "B" bands) are set aside for this type of operation. A full description of PCS operation is disclosed in U.S. Pat. No. 5,353,331 issued Oct. 4, 1994 to Emery et al., and assigned to Bell Atlantic Network Services, Inc. (a common assignee with that of the present application), incorporated herein by reference. The use of PCS as a third alternative is increasing in many locations and may some day be a standard third alternative to the existing "A" and "B" frequency bands.
The PCS handset has the capability of interfacing with a standard cellular base station, usually at the user's home, a local cellular system in which the user's home is located, additional cellular systems having access to the AIN, local microcell systems and any wireless Centrex/PBX to which the handset has been previously granted access. In order for the handset to gain access to the local cellular MC and microcell type PCS MC, both must be set up to transmit the same system ID (SID) and to indicate combined paging and access channels.
In order for the handset of the PCS to access its own base station as well as the macrocell MC and the microcell MC, the handset must operate at cellular frequencies. The scanning function of the handset is prioritized so as to register with its personal base station first. If the base station is not contacted the handset scans the macrocell and microcell control channels, selecting to register with the MC of the microcell system if detected before attempting to register with the MC of the macrocell system. If the handset has been granted access to a wireless Centrex system, it scans a set of control channels specially programmed into the handsets of Centrex members only. Selection of one of these special channels must be done by the specific action of the handset user, and additional handshake procedures may be carried out requiring a personal identification number (PIN) from the user before he or she is permitted to interface with the wireless Centrex.
The PCS home base station is structurally similar to prior art cordless telephone base stations, except that the transceiver in the base station operates at cellular frequencies and uses signalling protocols similar to those of the cellular network to perform registration procedures. Of particular note here, the base station includes a microprocessor for programmed control of base station operations. To perform registration with the ISCP, the base station also includes an auto dialer, and may include means to detect call progress tones and/or certain instruction signals from the telephone network.
The existence of additional types of systems such as the aforementioned PCS mode of communications further complicates the selection process as previously stated. Further, the power levels required for additional systems such as PCS may vary from the power levels required for the "A" and "B" cellular bands. Consequently, an increased range of power level becomes appropriate for subscriber station handsets. This, of course, increases control problems and the necessity for a predetermined coherent program of power control to optimize battery life in a cellular subscriber station handset.
The use of additional systems such as PCS also necessitate the acquisition by subscriber station handsets of additional control information pertaining to the available systems. The reasonable response to the existence of multiple available systems and modes of communication is the existence of multi-level, programmable power supplies in wireless subscriber handsets. Adjustable power supplies for servicing portable and mobile radio telephone units are well known in the conventional art. A number of examples are listed as follows.
U.S. Pat. No. 4,679,244 to Kawasaki et al. is directed to a method of transmitting terminating call signals within a restricted duration. This system also includes a base station in a portable unit arranged for particular use with the subject method. The system is arranged so that a portable unit may be called from a base station through a radio control channel by a succession of terminating call signals. The terminating call signals are sent through the control channel from the base station to portable unit for a first or restricted time duration (T.sub.1). This time duration is selected in consideration of a battery saving period calculated to save battery power within the portable unit. During the battery saving period, the portable unit is put into transient active and inactive states during a first time interval and a second time interval, respectively. The first time interval is longer than the second time interval so that the portable unit receives at least one of the terminating call signals during the first time interval. The base station monitors an acknowledgement signal for a second time duration (T.sub.2) after the lapse of the first time duration (T.sub.1), and interrupts the control channel when the acknowledgment signal is not received within the first and second time durations (T.sub.1, T.sub.2). In the portable unit, the battery saving operation is halted when the presence of the terminating call signal is detected by a squelch circuit. The effect of this operation is that the portable unit is periodically put into a transient active state and a transient inactive state by the battery saver circuit.
U.S. Pat. No. 5,109,530 to Stengel is directed to a radio receiver with a battery saving system. The receiver goes into a "sleep mode" in response to a monitored signal. The receiver is used for recovering modulation signals and includes a detector and a decoder for detecting the presence of a non-valid coded squelch signal and decoding such a signal in the recovered modulation signal. The receiver further includes a synchronizer for synchronizing the detected non-valid coded signal. The receiver is placed in a battery saving mode when a non-valid coded squelch signal is detected. The battery saver mode includes monitoring the recovered modulation signal for a change in the non-valid coded squelch signal. At which point, the battery saver mode ends.
U.S. Pat. No. 5,241,568 to Fernandez et al. is directed to a method and apparatus for synchronizing a receiver to transmit a signal while conserving power in that receiver. The method operates so that a receiver receives a transmitted signal having a first predetermined signal for indicating a start of a new transmission to the receiver. The transmitted signal has a second predetermined signal inserted at periodic sampling time intervals for synchronizing receiver to the transmitted signal. The receiver synchronizes to the transmitted signal by detecting the first predetermined signal followed by the second predetermined signal and establishing subsequent periodic sampling time intervals therefrom. The receiver manages to conserve power during a second portion of the periodic sampling time interval following the detection of a first portion of the second predetermined signal during a first portion of the periodic sampling time interval. If the receiver does not detect the first portion of the second predetermined signal, then the receiver searches for a portion of the first predetermined signal during the second portion of the periodic sampling time interval to determine a possible start of a new transmission. Power conservation can also be achieved by inhibiting the receiving circuitry, the decoding means and disabling other non-essential circuits and functions in the receiver during a "sleep cycle". Essentially, the receiver is shut down during certain preassigned frames.
U.S. Pat. No. 5,382,949 to Mock et al. is directed to a method for increasing battery life for selective call receivers. The selective call receiving system includes a base sight which transmits paging information having a plurality of batches. The base sight comprises a timer for calculating a time between a first of the least two successive paging transmissions and a counter for counting a number of batches to be transmitted in the subject paging transmissions. A base sight processor coupled to the timer counter processes the paging information. The base sight processor comprises an encoder for encoding a portion of the first of the successive paging transmissions with the calculated time and the number of batches to be transmitted in the first page in transmission. A base sight transmitter coupled to the base sight processor transmits the successive paging transmissions according to the calculated time to a plurality of selective call receivers. A selective call receiver comprises a receiver for receiving the paging transmissions, and a decoder coupled to the receiver for decoding the number of batches being transmitted therein, as well as a time to a next paging transmission. A power switch is coupled to the decoder for disabling and enabling a power supply to the receiver in order to receive an assigned frame of the plurality of transmission batches. The power switch is responsive to the plurality of batches being decoded so as to disable or enable the power supply to the receiver in order to receive successive paging transmissions.
U.S. Pat. No. 5,196,728 to Jaux is directed to a method of controlling a network of electronic stations. The method encompasses the use of a sleep mode when no active function of the network is indicated. In effect, the system is put into an active mode or a sleep mode based upon various electric loads placed upon the electrical system in a motor vehicle. The method operates to generate an activation signal in at least some of the stations in the network when a previously inactive function is requested. The system also generates a deactivation signal when an associated previously active function is to be deactivated. The system further operates to detect the generated activation and deactivation signals incrementing at least one counter by one step each time when the associated activation signal is detected. Likewise, the system operates to decrement the same counter by one step each time an associated deactivation signal is detected. A sleep signal is finally generated when a counter reaches a zero count after being decremented.
U.S. Pat. No. 5,140,698 to Toko is directed to a mobile telephone system with intermittent control of receiver components in a standby state. The mobile telephone system operates to send an intermittent signal to a power switch during a standby state so that power is turned on during the period when a necessary signal portion of a control signal derived from a signal receiving portion is input. The power switch is turned off during a period when an unnecessary signal portion of the control signal is input. Thus, the components of the signal receiving portion have short rise times and thus, short time intervals between the activation of the power source and the start of the operation. The use of intermittent power supplied to the system reduces power consumption.
U.S. Pat. No. 5,255,179 to Zekan et al. is directed to a switched mode power supply for a single-phased boost in the range of 1 kw to 10 kw AC. The power supply includes a DC-AC power converter which is connectable to a DC source and includes a first and second pair of switches which convert the DC source directly to AC. This is done by alternately switching between each of the first pair of switches at high frequency modulation and between the second pair of switches alternately switching at each of the half cycles of the low frequency fundamental output voltage. The result is a positive pulse train and a negative pulse train. A transformer boost is a source voltage to the desired high voltage of the output of the converter circuit. A filter is connectable to an AC load and has a plurality of damping modes for extracting fundamental frequency from the output of the transformer. The filter is operated responsive to a signal for switching between damping modes. A sine wave oscillator generates a sine wave at the fundamental frequency. Feedback circuits maintain the AC output at the fundamental frequency. Thus, the system is capable of generating a regulated DC output or a 60 Hz high voltage AC output.
U.S. Pat. No. 4,074,145 to Laffoon et al. is directed to an electric power generating apparatus incorporating an automobile alternator operable in a high voltage mode suitable for providing power for hand tools. The generator also operates in a low voltage mode suitable for maintaining the charge of a battery which provides a field current for the alternator. A switching circuit manually or automatically actuable to place the generator in the high voltage mode of operation interposes a voltage regulator in the field current circuit and connects the output of the alternator to the battery to charge the battery when the generator is operated in the low voltage mode. The switching circuit also interposes a variable resistor in the field current circuit and disconnects the battery from the output of the alternator to permit adjustment of the output voltage of the alternator when the generator is operated in the high voltage mode.
U.S. Pat. No. 5,175,439 to Harer et al. is directed to a power supply circuit for a motor vehicle. The power supply includes a 24 volt battery, a bidirectional converter, a combination of a starter/generator, and a rectifier/inverter. After start-up, the output of the generator is rectified by the diodes of the rectifier/inverter to provide 300 volts DC. A DC/AC inverter converts the 300 volt DC to 220 volts, 60 Hz AC. The bi-directional converter steps-down the 300 volt DC to 240 volt DC in order to provide power for other DC applications. An additional AC/DC rectifier supplies 5 volts DC -12 volts DC. The system also has the capability of providing 220 volts AC at 50 Hz.
U.S. Pat. No. 3,655,991 to Schneider is directed to a power output unit and a method for operating that unit to deliver constant frequency, constant voltage AC power. The power output unit is used as an accessory with an engine-powered vehicle having a conventional electrical system including a battery, voltage regulator and a dynamo which during normal operation supplies DC power to the vehicle electrical system. The system includes switches adapted to isolate the dynamo from the vehicle electrical system, and means for boosting the DC voltage output from the dynamo, as well as converting it to a constant frequency AC voltage. An outlet receptacle is provided to accept jacks from power tools or appliances having constant frequency AC voltage power requirements. The outlet receptacle voltage is monitored and the dynamo field current is adjusted in response to variations therein to control the dynamo voltage and the current input to the accessory unit.
U.S. Pat. No. 3,824,404 to Ghere is directed to a power output device for conversion of a vehicle alternator electrical system to supply electrical power for the operation of lighting fixtures, hand tools, etc. The power output means is connected to the normal vehicle ignition and includes a master switch connected to a voltage control assembly and current control assembly to achieve a power output at an output receptacle. The power output receptacle is regulated regardless of the vehicle engine speed.
Many of the aforementioned examples of multi-power level power supplies are programmable and thus, can accommodate a variety of power levels commensurate with different operating modes. However, none of the aforementioned systems is programmed to optimize power use in the selection of operating bands for a roaming wireless subscriber. Nor is there any conventional program or arrangement in selecting the operating mode most appropriate for a particular communications activity in order to increase battery life. Such optimization programs would greatly reduce unnecessary power use and thus, increase battery life for wireless cellular subscriber station handsets.